Since 1979 a new Acquired Immune Deficiency Syndrome has been observed in homosexual and bisexual males, male and female intravenous drug abusers, male and female Haitians, hemophiliacs, and intimate contacts of the aforementioned. Immunologically, the Acquired Immune Deficiency Syndrome is marked by a devastating depression in cellular immune function with subsequent development of multiple severe opportunistic infections. This project involves the evaluation of open lung biopsy, transbronchial biopsy, bronchial brush and bronchial lavage for the diagnosis of Pneumocystis carinii penumonia in these patients.